1-Alkyl-3-haloalkyl-5-fluoropyrazolecarbaldehydes and esters thereof are important building blocks for preparing plant protection active ingredients, particularly SDHI fungicides.
1-Alkyl-3-difluoromethyl-5-fluor-1H-pyrazole-4-carbaldehydes was so far typically prepared in a multi-stage transformation starting from difluoromethylacetoacetate (WO 2011061205):

Starting material for this transformation, i.e. ethyldifluoracetoacetate, is a rather unstable compound, difficult to purify and which loses its quality during storage. This makes the utilization of this compound, especially on industrial scale, difficult.
The transformation of pyrazolic compounds bearing CF2H group is a challenging task as well, since this group is rather unstable under acidic conditions and easily releases fluoride which can damage reaction vessel, especially on a technical scale.
A process for the preparation of esters of 1-alkyl-3-fluoroalkylpyrazole-carboxylic acids via the reduction of 3-chlorodifluoromethylpyrazolic carboxylates was known from WO 2012/010692. Nevertheless, it was not known nor expected that a reductive dehalogenation of CF2Cl-group can occur in pyrazoles bearing a halogen atom in position 5 or a carbaldehyde function in position 4 without undesirable effect on said halogen atom in position 5 or carbaldehyde function in position 4. On contrario, the skilled man would expect that the aldehyde group will also at least partially react, and/or that the fluorine atom in position 5 will also at least partially react, as it is shown or suggested in WO 2013/171134 and WO 2004/063165. Indeed WO 2013/171134 shows the reductive elimination of the halogen atom in position 5 of 5-chloro-1-alkyl-3-difluormethylcarbaldehyde, and WO 2004/063165 describes the removal of a chlorine atom in N-aryl-3-methyl-5-chloropyrazole-carbaldehydes.